The present invention relates to a novel absorption refrigerator and, more particularly, to an absorption refrigerator which has excellent corrosion resistance properties, with main structural components of the absorption refrigerator being highly protected from corrosion by forming in advance corrosion protective films on surfaces of the main structural components, and the invention relates to a method of manufacture of the absorption refrigerator.
Absorption refrigerators each use a rich LiBr solution as an absorption solution and water as a refrigerant. In the absorption refrigerator, in general, the higher the concentration of the LiBr solution is, the higher the efficiency of refrigeration becomes, so that the concentration and temperature of the LiBr reach to 65% and 160.degree. C., respectively, at the highest temperature portion of a double effect absorption refrigerator, for example. Under such circumstances, the structural members of the refrigerator tend to become seriously corroded. Therefore, a suitable inhibitor, such as tungstate, molybdate has been added to the solution, as disclosed in JP A 58-224186 and JP A 58-224187, whereby corrosion has been reduced. The inhibitor is used together with the hydroxide of an alkaline metal, which is a pH adjuster and forms corrosion protective films on the members due to the oxidizing force thereof, whereby corrosion is suppressed.
Apart from a method of forming a corrosion protective film during operation of a refrigerator, there is a method in which, as disclosed in JP A 1-121663, JP A 2-183778, in order to form a corrosion protective film on an inner wall of a high temperature regenerator, in contact with a most highly corrosive absorption solution therein before operation of the refrigerator, a film forming liquid recirculation line and a refrigerant supply line are provided in the high temperature regenerator, and a film coating operation is carried out by recirculating a film forming liquid, heated and concentrated in the high temperature regenerator, through the film forming liquid recirculation line, whereby corrosion protective films are coated on the inner wall of the high temperature regenerator and the surfaces of the piping of the recirculation lines which are in contact with the absorption solution.
Further, as a corrosion protective film coating method which does not use an absorption solution, there is a method in which a corrosion protective film is formed in the interior of a refrigerator by heating it to 400.degree. C. or more under a gas atmosphere in which the dew point thereof is controlled so that the partial pressure of steam becomes 10 ppm or less and the partial pressure of oxygen is adjusted to about 10 Pa-10 kPa, as disclosed in JP A 6-249535.
As for a method of forming a corrosion protective film using an inhibitor during operation of a refrigerator, in a case wherein chromate and nitrate are used as the inhibitor, it is feared that pitting may occur in the structural material when the concentration of the inhibitor reaches a certain level or more, and so there remains a problem of management of the inhibitor concentration when an inhibitor is used. On the other hand, since molybdate has a low solubility to LiBr and the oxidation is weak, there remains a problem in that much time is required to form a stable corrosion protective film, and the refrigeration efficiency decreases due to generation of hydrogen gas during formation of a stable corrosion protective film, whereby it is difficult to attain a sufficient corrosion protective effect. Further, a relatively large amount of inhibitor is consumed by the time a stable corrosion protective film is completed, so that it is necessary to add inhibitor.
As disclosed in the above-mentioned prior methods, there is a method of forming a corrosion protective film by performing a film forming operation using a film forming liquid recirculation line before operation of the whole refrigerator, in order to solve the above-mentioned problems. In this method, however, since the film forming liquid used in the film forming operation is a LiBr solution including molybdenum, as used in the method of forming a corrosion protective film during operation of the refrigerator, the problem of a decrease in refrigeration efficiency due to generation of hydrogen gas during the operation can be solved, however, other problems are still left unsolved in that much time is required for forming a corrosion protective film due to the low solubility of molybdate, the fact that the oxidation also is weak, and in that much inhibitor is consumed.
The corrosion protective film formation method which does not use an absorption solution and is disclosed in the above-mentioned prior art can solve the problem that much time is required to form a corrosion protective film because of the low solubility of molybdate and the weak oxidation, and the problem that a relatively large amount of inhibitor is consumed. However, the step of injecting an inert gas in order to control the dew point, the step of condensing steam to lower the pressure to a prescribed level or lower, the step of injecting oxygen gas to a prescribed pressure, etc. are needed, so that the corrosion protective film forming method becomes not only complicated, but various apparatuses are required, such as a vacuum pump, a pressure gauge, a mass analyzer, a cold trap, etc., and so the refrigerator becomes complicated in construction and high in cost. Further, in a method in which an interior of a refrigerator first is filled with an inert gas (since the inert gas is introduced after reduction of the pressure, the inert gas is replaced with gas in the entire interior of the refrigerator) and then oxygen gas is injected, even if oxygen is caused to flow therein, the oxygen gas does not enter all gaps and convection portions in the interior of the refrigerator, so that it is difficult to make the partial pressure of oxygen uniform in the refrigerator. Therefore, in some portions, a corrosion protective film is formed by excessive oxygen, but some other portions lack oxygen, so that a sufficient corrosion protective film is not formed or an incomplete corrosion protective film is formed, and so corrosion is not suppressed.